1. Field of the Invention
This invention relates generally to the field of geological exploration for hydrocarbons. More specifically, the invention relates to a method of determining wettability of rock samples.
2. Background of the Invention
Wettability is a property of rocks which measures the preference of a fluid such as oil, gas, or water, to be in contact with the surface of a rock pore. The pore surface may be a mineral or a mineral which is partially or completely coated with a hydrocarbon material and/or “heavy organic materials.” For the purposes of this disclosure, these “heavy organic materials” are highly viscous and/or semi-solid hydrocarbon materials. Examples of heavy organic materials include, for example and without limitation, bitumen, resins, asphaltenes, and pyrobitumen. Bitumen is organic matter soluble in organic solvents, such as carbon bisulfide. Asphaltene is organic matter that is insoluble in straight-chain solvents, such as pentane or heptane. Resin molecules are aromatic ring hydrocarbons. Pyrobitumen is insoluble, thermally altered bitumen or oil. To be clear, as used herein, heavy organic materials are to be distinguished from lighter, less viscous hydrocarbon crude oil components such as alkanes, naphtalenes, aromatics, etc. As used herein, these lighter, less viscous or lighter hydrocarbon crude oil components will be referred generically as “light hydrocarbon materials.” Typically, for rock or core samples obtained from a reservoir, wettability is determined for a very small number of samples. Limited results are generally extrapolated to large volumes of rocks. Wettability is a parameter which has an impact on a number of reservoir project economics. For example, wettability influences oil recovery from a reservoir. Additionally, wettability has an effect on waterflood and gasflood performance.
Consequently, there is a need for improved methods and systems to determine wettability of rock samples from a reservoir.